Table of Content

15 October 2024, Volume 53 Issue 10

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Invited

Research Progress on Gallium Garnet Series Single Crystal with Large Lattice Constant for Magneto-Optical Substrates

LI Hongyuan, SUN Dunlu, ZHANG Huili, LUO Jianqiao, QUAN Cong, CHENG Maojie

2024, 53(10):  1657-1668. 

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With the rapid advancement of optical communication technology and integrated electronic devices, magneto-optical thin films, particularly rare earth iron garnet (RIG), have emerged as the most promising materials for near-infrared communication windows in recent years. In order to minimize the impact on the related properties of magneto-optical thin films during the preparation process, it’s important to select the substrate materials. Silicon and garnet oxides are commonly used as substrates for the preparation of RIG magneto-optical thin films. The lattice constant of RIG magneto-optical thin films is generally around 12.4 Å, and gallium-containing garnet oxide single crystal substrates have a similar lattice constant, which shows large lattice constant characteristics, making them one of the suitable substrate materials. However, the raw material gallium oxide is volatile at high temperature, the preparation of gallium-containing garnet single crystal has been a hot topic. The further study of gallium garnet series substrate single crystals is expected to promote the development of a new magneto-optical devices. In this paper, we reviewed the research of gallium garnet series single crystal, summarized the work of our team in the growth, structure and key parameters of these crystals, and outlooked the trend of research and development.

Research Letter

Growth of 2-Inch Ytterbium-Doped Calcium Niobium Gallium Garnet Single Crystal by Bridgman Method

ZHOU Lintao, ZHAO Tao, SUN Zhigang, JIANG Linwen, PAN Shangke, PAN Jianguo, ZHENG Yanqing

2024, 53(10):  1669-1674. 

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In this paper, 4.2% ytterbium-doped calcium niobium gallium garnet (Yb∶Ca₃(NbGa)₅O₁₂) crystals with diameter of 2 inch (1 inch=2.54 cm) were grown by Bridgman method. The obtained crystals were intact and free of visible defects. Crystal structure was determine by XRD, which reveals that the crystal belongs to the cubic crystal system with lattice parameters a=b=c=12.493 Å. The crystals were oriented and cut to obtain some (420) plane wafers with dimensions of 10 mm×10 mm×1 mm. These wafers were double-side polished to obtain the final samples. The performance of the samples was characterized through X-ray diffraction, ultraviolet-visible spectrophotometer, and fluorescence spectroscope. The results show that the rocking curve of the crystal has a full width at half maximum (FWHM) of 43″, and the transmittance reaches 80% in the near-infrared wavelength range. At 935 nm, FWHM of the absorption peak is 47.15 nm and absorption cross-section is 1.53×10^-20 cm². When excited with a 980 nm laser, an emission peak was observed at 1 031 nm, corresponding to the transition of Yb³⁺ from the excited state ²F_5/2 to the ground state ²F_7/2.

Review

Research Progress in Chemical Mechanical Polishing of Diamond

AN Kang, XU Guangyu, WU Haiping, ZHANG Yachen, ZHANG Yongkang, LI Lijun, LI Hong, ZHANG Xufang, LIU Fengbin, LI Chengming

2024, 53(10):  1675-1687. 

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Diamond plays a significant role in the fields of mechanics, optics, thermology and electronics (such as semiconductors) with its excellent properties. However, the surface quality of diamond affects its application in these areas. Therefore, obtaining high-quality surfaces through efficient polishing technology has always been a focus of diamond research. The main diamond polishing technologies include mechanical polishing, thermochemical polishing, laser polishing and chemical mechanical polishing, among which chemical mechanical polishing (CMP) has the advantages of low equipment operating costs, simple process, and minimal surface damage after polishing. Based on the analysis and comparison of the above polishing methods, this paper focuses on the field of CMP and makes a detailed comparison and analysis of its development history. Although the early CMP technology had certain limitations in process and polishing efficiency, it lays the foundation for the innovation and optimization of the subsequent technology; the application of H₂O₂ and its mixtures not only enhances the chemical reaction activity in the process of CMP and improves the material removal rate, but also effectively reduces the surface roughness and improves the surface quality of diamond; the photocatalytic assisted chemical mechanical polishing can enable diamond to achieve a high surface quality, but the equipment is relatively complicated and cannot meet the demand of mass production, which needs further research and optimization. In addition, this paper also predicts the future development of chemical mechanical polishing to provide reference for researchers in related fields.

Research Articles

Spectral Properties of Concentration Gradient Yb∶YAG Laser Crystals Grown by Horizontal Directional Crystallization Method

DING Yuchong, ZHANG Ling, LI Hailin, ZHANG Yue, TANG Yang, QIANG Ming, LIN Hui

2024, 53(10):  1688-1698. 

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A concentration gradient Yb∶YAG laser crystal with a size of 180 mm×81 mm×16 mm was grown by horizontal directional crystallization (HDC) method. Four crystal pieces with the size of 40 mm×40 mm×7 mm and 70 mm×70 mm×7 mm (two pieces for each size) were taken from the shoulders and tails of the single crystal plate, respectively. A 632 nm laser and a polarizing stress meter was used to characterize the samples’ optical properties. From the results, it can be seen that compared to the crystals near the crucible, the crystals near the surface are more transparent, with no scattering light path, and showing lower and more uniform stress. The crystal was also subjected to absorption spectra measurement, and its absorption coefficient at 935 nm wavelength was used to calculate the doping concentration of Yb³⁺ at different positions in the crystal. It was found that the Yb³⁺ doping concentration in laser crystal plates with a size of 40 mm×40 mm×7 mm gradually increased along the crystal growth direction, with a concentration gradient of approximately 0.42%/cm. The Yb³⁺ doping concentration in laser crystal plate with a size of 70 mm×70 mm×7 mm remains almost unchanged, which is approximately 4.50%.

Growth and Magnetic Properties of GaFeO₃∶Mg Crystals

WANG Wenkai, PAN Xiuhong, HU Yuqing, LIU Xuechao, CHEN Xiaohong, CHEN Kun, FANG Jinghong, HE Huan, NI Jinqi

2024, 53(10):  1699-1704. 

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Multiferroic materials can realize the mutual coupling between force, electricity, magnetism and other physical fields, and have important application prospects in the field of small size, fast response and low power consumption of magnetoelectric devices. GaFeO₃ is a highly promising multiferroic material featuring high spontaneous magnetization and polarization beyond room temperature. In this study, Ferroelectric Mg_xGa_1-xFeO₃ (x=0.02, 0.05, 0.07 and 0.10) single crystals with a diameter of about 7 mm were grown by light floating zone method. The effect of Mg²⁺ on the saturation magnetization and magnetic transition temperature of GaFeO₃ (GFO) crystals were studied. The structure and phase of the crystal were analyzed through XRD, the results show that all the prepared samples correspond to the diffraction characteristics of the standard crystal card library GFO (PDF#76-1005), and no other heterophase appears. The XRD refinement results indicate that, the crystal structure is orthogonal and its space group is Pna2₁. As the concentration of Mg²⁺ rises, the lattice constant and cell volume initially increase and subsequently decrease. Additionlly, the magnetic properties of the crystal were studied through a comprehensive physical property measurement system, the magnetic transition temperature and saturation magnetization of the grown crytals also increase firstly and then decrease with the increase of Mg²⁺ doping content. When the Mg²⁺ doping amount is 0.07, the magnetic transition temperature and saturation magnetization reach the maximum values of 187.82 K and 8.75 emu/g, respectively, which achieves the purpose of doping modification.

Effect of Thermal Treated GaSb Substrate for Epitaxial Growth of CdZnTe Film by Close-Spaced Sublimation Method

LI Yang, CAO Kun, JIE Wanqi

2024, 53(10):  1705-1711. 

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The surface quality of the substrate has an important effect on the quality of the growth film. The roughness, uniformity, adhesion residue and oxide layer of the substrate are the evaluation criteria of its surface performance. In this paper, an in-situ thermal treatment method to remove the natural oxides on GaSb (001) substrates for epitaxial growth of CdZnTe films by close-spaced sublimation method was reported. By controlling the temperature and time of the thermal treatment, a clean and smooth substrate state is obtained. The effect of thermal treatment on the morphology and composition of GaSb substrate was analyzed by atomic force microscopy and X-ray photoelectron spectroscopy. The crystal quality of CdZnTe epitaxial film grown on GaSb substrate after thermal treatment was evaluated by double crystal X-ray curve. In order to further study the properties and epitaxial formation mechanism of the micro-defects near the heterogeneous interface, TEM analysis of CdZnTe/GaSb cross section was also carried out. After 180 s thermal treatment at 600 ℃, the GaSb substrate can obtain a clean and relatively flat surface after most of the oxide is removed from the substrate surface, thus improving the crystallization quality of CdZnTe epitaxial film. The full width of half maximum of double crystal X-ray curve is 94″, which approached the crystalline quality of bulk CdZnTe crystal ever reported.

Preparation and Epitaxy Application of 8 Inch SiC Wafers

HAN Jingrui, LI Xiguang, LI Yongmei, WANG Yaohao, ZHANG Qingchun, LI Da, SHI Jianxin, YAN Honglei, HAN Yuebin, TING Hungkit

2024, 53(10):  1712-1719. 

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Silicon carbide (SiC) is one of the superior materials used in the manufacture of electronic components designed to work at high temperatures, high frequencies and high-power. In the past two decades, the application of SiC materials has been expanding as a result of much improved production and processing techniques. Although most SiC chips are still mainly made from 6 inch (1 inch=25.4 mm) wafers, leading manufacturers have begun developing next-generation parts and chips based upon 8 inch SiC wafers. This study collaborates with leading enterprises in the upstream and downstream of the domestic silicon carbide industry chain in order to facilitate domestic production of 8 inch SiC chips, with the focus being wafer preparation and epitaxial growth. In this work, 8 inch conductive 4H-SiC substrate wafer was prepared by diameter expansion growth, with low average base plane dislocation (BPD) density (251 cm^-2) and virtually ‘zero threading screw dislocation (TSD)’ density (<1 cm^-2) that meet the production requirements. Based on these 8 inch substrates, we achieve fast epitaxial growth (68.66 μm/h) with domestically produced 8 inch epitaxy equipment and processing packages. The thickness uniformity of the resultant wafers is 0.89% and the doping uniformity is 2.05%. These parameters, as well as the defect density, are on par with those of high-quality 6-inch wafers, fully meeting production requirements. The 8 inch wafers prepared in this paper are better than those described in international publications in terms of thickness and doping uniformity. The defect density is only 1/4 of international data. In this paper, multi-wafer repetative text was designed and executed, to verify the stability of 8 inch epitaxy.

Design of Two-Dimensional Layered Phononic Crystal Structures Based on LightGBM and Genetic Algorithm

CHU Fan, ZHAO Chunfeng

2024, 53(10):  1720-1728. 

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Phononic crystals are periodically artificial composite structures that have garnered widespread attention for their bandgap properties and potential applications in wave propagation control, offering novel solutions for engineering vibration and noise reduction. The design of these materials is a current research focus. This study takes two-dimensional layered phonon crystal structure as an example, presents an innovative method for designing two-dimensional layered phononic crystal structures, utilizing LightGBM and an improved genetic algorithm. Initially, the LightGBM algorithm was employed for bandgap prediction of the phononic crystals, with the structural arrangement vectors subjected to categorical feature processing, and hyperparameter tuning conducted through the simulated annealing algorithm, achieving a prediction accuracy with an overall error of no more than 2% within 1/3134 of the traditional finite element method computation time. Subsequently, a design method integrating a genetic algorithm based on an elite preservation strategy was introduced. Using the environmental vibration issue caused by subway operation as an example, a fitness function optimized for bandgap width was established, resulting in a population with structural bandgaps covering the 30~40 Hz frequency range. Finally, finite element analysis of one structure verified its bandgap characteristics align closely with expectations. This research provides a new solution for the efficient optimization design of multiple phononic crystal structure schemes.

Preparation and Photoelectric Properties of Co₃O₄@BiVO₄ Composite Thin Films

CONG Wenbo, PENG Shaolong, WANG Hang, LI Lihua, HUANG Jinliang

2024, 53(10):  1729-1737. 

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In this paper, FTO conductive glass was used as a substrate to successfully prepare Co₃O₄ thin films with controlled morphology by hydrothermal method. Using the prepared Co₃O₄ thin films as the base, Co₃O₄@BiVO₄ composite thin films with varying amounts of BiVO₄ were successfully prepared by controlling the number of spin-coating cycles. The phase composition and microstructure were analyzed using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). Additionally, their optical absorption and photoelectric properties were measured using a UV-3600 UV-Vis spectrophotometer and an electrochemical workstation. Results indicate that, based on the XRD patterns of the Co₃O₄@BiVO₄ composite thin films, the composite materials were successfully prepared. From the FESEM images, it can be observed that the prepared Co₃O₄@BiVO₄ composite thin films possess a continuous, uniform, and dense surface, with the Co₃O₄ thin films growing uniformly as nanowires, and the spin-coated BiVO₄ uniformly coating the surfaces of Co₃O₄ nanowires in a block-like manner. The optical absorption spectrum reveals enhanced light absorption of the Co₃O₄@BiVO₄ composite thin films compared to pure Co₃O₄ thin films. Under zero bias voltage and illumination, the photoelectrical performance of the Co₃O₄@BiVO₄ composite thin films surpasses that of pure Co₃O₄ thin films. Electrochemical test results demonstrate that the Co₃O₄@BiVO₄-3 composite thin films, which were spun-coated three times, showing optimal photoelectrical performance, with a maximum photocurrent approximately 18.4 times that of pure Co₃O₄ thin films. The responsivity of the device is 105.5 μA/W, with a detectivity of up to 1.988×10¹¹ Jones.

Laser-Induced Damage Characteristics of VO₂-SiO₂ Composite Films

HAN Sun, LI Yan

2024, 53(10):  1738-1744. 

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The VO₂ and VO₂-SiO₂ composite films were prepared by sol-gel method. The phase structure and transmittance of films were characterized by X-ray diffraction (XRD) and ultraviolet visible spectrophotometer. The results reveal that the prepared VO₂ film is monoclinic phase (B), and the XRD patterns of VO₂-SiO₂ composite film is similar to that of VO₂ film. The optical transmittance of films have reached over 90% within the range of 450 nm to 800 nm. The laser induced damage threshold (LIDT) of VO₂-SiO₂ composite film is 3.9 J/cm², which is 77.3% higher than that of VO₂ film. The difference in damage morphology between VO₂ film and VO₂-SiO₂ film were studied by FESEM and step analyzer. The VO₂ film exhibits melt type damage, while the VO₂-SiO₂ film exhibits melt type damage and stress damage. In addition, laser-induced damage models for different films were constructed and damage characteristics and underlying mechanisms were discussed.

Characterization of Micro-Scratches on 4H-SiC Substrates by KCl Solution Crystallization-Assisted Method

ZHANG Chitengfei, ZHANG Song, GONG Ruocheng, YANG Junwei, SONG Huaping

2024, 53(10):  1745-1751. 

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Micro-scratches on 4H-SiC wafers can transform into dislocations, stacking fault and other type of defects during homoepitaxial process, leading to reduce yield of epitaxial wafers. These micro-scratches are challenging to detect using non-destructive optical characterization methods due to their ultra-thin line width, which is beyond the resolution of current optical technology. A novel method has been developed to reveal these micro-scratches, which are typically invisible under optical microscopy, on SiC wafers after chemo-mechanical polishing (CMP) treatment. This method is based on the classical nucleation theory, and KCl crystals preferentially nucleate on high-index crystallographic facets with high surface energy during the KCl solution drying process. The experimental results show that the KCl crystals could embed in the ravines of the micro-scratches at a KCl solution concentration of 0.013 mol/L, allowing for their indirect detection by optical microscopy. When the concentration of KCl solution is greater than 0.013 mol/L, lots of KCl crystals crystallize on the areas without micro-scratches and interfere with the characterization of micro-scratches. KCl crystals formed by this method can be removed from the surface through the RCA cleaning process without impacting the subsequent wafer processing, because they are adsorbed and nucleated on the surface of 4H-SiC without undergoing any chemical reaction with SiC substrates.

Electric Field Modulated Electronic Properties of Two-Dimensional Metal-Organic Framework: First-Principles Study

YANG Yan, WANG Xianlang, CHEN Haotian, LU Hao, SHE Shixiong, HUANG Zhihao

2024, 53(10):  1752-1758. 

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Based on density functional theory (DFT), a two-dimensional(2D) metal-organic framework (MOF) based on Co and Cu atoms were presented. Based on the phonon dispersion calculations, no imaginary mode is found in the phonon branches, which verifies that the crystal structures of MOF could be stable. Based on the calculation of electronic band structure, it is found that the Cu-based MOF is a metallic system by applying external electric field. While the Co-based MOF undergoes a transition from metal to semiconductor under external electric field. When the external electric field intensity reaches up to 0.5 eV/Å, the band gap of Co-based MOF is around 0.1 eV, while this does not happen in the Cu-based MOF. Furthermore, the N₂ adsorption and the nitrogen reduction reaction (NRR) were investigated for the Co-based MOF, which shows that the NRR for the Co-based MOF exhibits good performance, and the electric field could enhance this effect of NRR. The free energy of NRR under external electric field of 0.5 eV/Å is 0.51 eV lower than that without electric field. Therefore, our study would prospectively guide the experimental researchers on the design of NRR.

Preparation and Spectral Properties of La₂Mg_4/3Sb_2/3O₆∶Mn⁴⁺ Red Phosphor for Plant Growth Illumination

SONG Mingjun, YU Dianchen, WANG Jing, ZHOU Weiwei, ZHAO Wang

2024, 53(10):  1759-1768. 

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A series of La₂Mg_4/3Sb_2/3-xO₆∶xMn⁴⁺ red phosphors were prepared via traditional high-temperature solid-reaction method, and their structure, morphology and spectral properties were investigated. The results show that La₂Mg_4/3Sb_2/3O₆ belongs to the double-perovskite structure as La₂Mg_4/3Nb_2/3O₆ does, and the incorporation of Mn⁴⁺ has no influence on the structure of the phosphors. La₂Mg_4/3Sb_2/3-xO₆∶xMn⁴⁺ phosphor exhibits two broad excitation bands at 360 and 510 nm, corresponding to the ⁴A_2g→²T_2g and ⁴A_2g→⁴T_2g transitions of Mn⁴⁺ respectively. Upon 360 nm excitation, La₂Mg_4/3Sb_2/3-xO₆∶xMn⁴⁺ phosphor gives rise to a intense red emission band at 710 nm, which belongs to the ²E_g→⁴A_2g transition of Mn⁴⁺. The optimal concentration of Mn⁴⁺ in La₂Mg_4/3Sb_2/3O₆ host was determined to be 0.004, with quantum yield and color purity up to 89.6% and 99%, respectively. A crystal field analysis for Mn⁴⁺ in the La₂Mg_4/3Sb_2/3O₆ matrix was conducted based on the excitation and emission spectra, and the crystal field parameters D_q, B and C were calculated. The temperature quenching process of La₂Mg_4/3Sb_2/3-xO₆∶xMn⁴⁺ phosphor was analyzed with the configurational coordinate diagram of Mn⁴⁺, and the activation energy was calculated to be 0.355 eV. Finally, a comparison between the emission spectra of La₂Mg_4/3Sb_2/3-xO₆∶xMn⁴⁺ phosphor and the absorption spectra of phytochrome P_R and P_FR was provided, and the application prospect of La₂Mg_4/3Sb_2/3-xO₆∶xMn⁴⁺ phosphor in LED plant illumination was preliminarily evaluated.

Synthesis, Crystal Structure, Luminescent and Magnetic Properties of Pyridyl Phenyl Substituted Nitronyl Nitroxide Radical-Mn^II-Ln^III Tetranuclear Clusters

LI Baoyi, HE Min, LI Hongdao

2024, 53(10):  1769-1775. 

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5-(4-pyridyl) phenyl substituted functionalized nitronyl nitroxide biradical ligand holds Mn^II ions and Tb^III/Ho^III ions together to yield 3d-4f-biradical heterospin clusters, namely, [Ln₂Mn₂(hfac)₁₀(NITPhPybis)₂] [Ln=Tb 1, Ho 2], wherein, two NITPhPybis radicals ligate two Mn^II ions via two NO groups and two nitrogen-atoms from pyridine rings. At the same time, each NITPhPybis encapsulates one Ln^III ion through chelating mode with adjacent NO groups, generating an annular centrosymmetric heterometallic tetranuclear system. In addition, the direct current and alternating current magnetic properties and luminescent behavior were systematically studied. Magnetodynamic studies uncover that the cluster 1-TbMn exhibits slow magnetic relaxation. The fluorescence of two polynuclear clusters show the characteristic fluorescence of Tb^III or Ho^III ions.

Synthesis and Solid-State Luminescence of Mn(II) Complex Constructed by 2-Naphthalic Acid/1,10-Phenanthroline

REN Nana, JIANG Xuying, SONG Hexing, SHI Fulin, WANG Yaru, SUN Zan

2024, 53(10):  1776-1783. 

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A case of binuclear manganese complex [Mn₂(L)₄(phen)₂(H₂O)₂] (1) was synthesized under solvothermal conditions with 2-naphthalic acid (HL) and 1,10-phenanthrenoline (phen) as ligands and manganese carbonate as the metal source. Complex 1 was characterized by single-crystal X-ray diffraction, elemental analysis, fourier transform infrared spectroscopy, powder X-ray diffraction, and thermogravimetric analysis. single-crystal X-ray diffraction shows that complex 1 belonged to the triclinic crystal system P1 space group and the crystal cell parameters are a=0.769 89(5) nm, b=1.175 86(5) nm, c=1.668 30(9) nm, and α=107.074(5)°,β=96.167(5)°,γ=106.901(5)°. The asymmetric unit consists of a manganese ion, two 2-naphthoate anions, one 1,10-phenanthroline ligand and one water molecule, and Mn(II) atom is in a distorted octahedral configuration. The asymmetric units are bridged by carboxyl-oxygen atoms to form a dinuclear structure and then the binuclear structures are linked into a 2D supramolecular structure through π…π stacking interactions. The results of fluorescence spectroscopy show that complex 1 has good fluorescence performance and the maximum emission wavelength is 416 nm (λ_ex=302 nm). Thermogravimetric analysis shows that complex 1 remains stable to 117 ℃, and then begins to lose water of 3.18%, the structure after dehydration can stabilize at 223 ℃, after which the organic framework begins to collapse. Hirshfeld surface analysis is used to study the interaction between molecules.

Synthesis, Single Crystal Structure, and Magnetic Study of Divalent Metal Nickel Magnetic Complex

AN Yanyan, GUO Tingting, BIAN Jianhong, ZHAO Dan, YAN Juanzhi

2024, 53(10):  1784-1790. 

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The synthesis of a novel complex [Ni₃(L^3-)₂(1,4-bib)₄(H₂O)₂]·5H₂O (1) with three-dimensional framework structure was achieved through a hydrothermal reaction, employing 5-((4-carboxylphenoxy)-methyl) isophthalic acid (H₃L) as the main oxygen-containing ligand, complemented by the N-donor ligand 1,4-bis(1H-imidazol-1-yl)benzene (1,4-bib), and Ni(II) ions. The structure of complex 1 was characterized by single crystal X-ray diffraction, powder X-ray diffraction, and elemental analysis. Complex 1 is crystallized in the triclinic crystal system of P-1 space group, and its crystallographic parameters are a=1.260 5(7) nm, b=1.349 1(7) nm, c=1.364 8(7) nm, α=111.913(8)°, β=117.251(7)°, γ=90.732(8)°, V=1.866 2(18) nm³, Z=1, M_r=1 769.66, F(000)=916, μ=0.84 mm^-1, D_c=1.575 mg·m^-3, S=1.06, R₁=0.056, wR₂=0.159. The joint contribution of semi-rigid tricarboxylic acid ligand L^3-, rigid 1,4-bib and also with Ni(II) ion to form a predictable high-dimensional structure. Complex 1 is a three-dimensional network constructed through the coordination of N and O atoms with Ni ion and the structural extension of the ligand. In addition, the magnetic properties of Ni(II) compound containing single d electron center were studied: the carboxyl group in mononuclear complex 1 only binds to one cation, resulting in magnetism in the solid being determined by the behavior of single metal ions. Variable temperature magnetic susceptibility of χ_mT in complex 1 can be described by zero field splitting.

Synthesis, Structure and Photocatalytic Properties of a Cobalt Complex Constructed by Dipyridyl-Diamide Ligand

XU Zhixiang, AN Zhixuan, LI Yuyao, SUN Chang, LI Xiaohui

2024, 53(10):  1791-1797. 

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In this paper, a semi-rigid dipyridyl-diamide ligand was selected as the organic linker to assemble with CoCl₂, and a new cobalt complex [Co(EDPB)Cl₂] (EDPB=(E)-4,4′-(ethene-1,2-diyl)bis(N-(pyridin-3-yl)benzamide)) was prepared under the solvothermal conditions. The structure and properties of the complex were tested by single crystal X-ray diffraction, powder X-ray diffraction, infrared spectra, thermogravimetric analysis, and solid-state UV-Vis diffuse reflectance spectra. It is found that the Co(II) atoms in the complex are tetracoordinated, which connect with EDPB ligands to form a 1D chain structure. The complex exhibits excellent absorption for visible light and highly heterogeneous catalytic activity for Cr(VI) reduction reaction with 97.9% of reduction rate in 60 min. The complex’s ability to be recycled for photocatalytic Cr(VI) reduction reaction was examined. Remarkably, it can be reused at least five times without any degradation in activity, showing its excellent cycling stability.

Preparation and Photocatalytic Performance of Bi_1-xLa_xFe_1-yMn_yO₃

LI Yanmei, ZHANG Jiarui, KUANG Daihong, YANG Jiadong, AWABAIKELI Rousuli

2024, 53(10):  1798-1808. 

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Using citric acid as a chelating agent, BiFeO₃ nanopowders doped with La at the A-site, Mn at the B-site, and co-doped with La/Mn were synthesized through an ultrasonic-assisted sol-gel method. Characterization techniques such as X-ray diffraction (XRD), ultraviolet visible diffuse reflectance spectroscopy (UV-DRS), X-ray photoelectron spectroscopy (XPS), specific surface area and pore size analysis (BET), and photoluminescence spectroscopy (PL) were employed to analyze the morphology, structure and elemental composition of Bi_1-xLa_xFe_1-yMn_yO₃ crystals. The results indicate that doping with La and Mn elements can significantly alter the crystal structure and morphology of BiFeO₃, suppressing the recombination of its charge carriers. Using Bi_1-xLa_xFe_1-yMn_yO₃ as a photocatalyst, the effects of pH value and light source on the photocatalytic degradation of simulated pollutants were investigated, and further experiments to explore the photocatalytic mechanism were conducted. The results reveal that La/Mn co-doped samples show significant differences in degradation rates for congo red (CR) and methylene blue (MB), which is related to the electronegativity of the dye molecules. Meanwhile, doping enhances the magnetic properties of the samples, which is beneficial for recycling and improving its utilization efficiency.

Preparation and Characterization of UiO-66-NH₂ Composite Sulfonated Polyphosphazene Proton Exchange Membranes

FU Fengyan, GAO Zhihua, WANG Yan, WANG Xiaohong, ZHANG Li, WANG Pei, LIU Yanbin

2024, 53(10):  1809-1814. 

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Metal organic framework (MOF) materials have attracted widespread attention due to their tunable structure, high porosity, and large specific surface area. MOF modified with functional groups were introduced into ionic polymers that could provide proton conduction, which could prepare proton exchange membranes with high proton conductivity. In this paper, UiO-66-NH₂ were introduced into sulfonated polyphosphazene (SPFPP) to prepare composite proton exchange membranes, the thermal stability, swelling degree, water uptake, and proton conductivity were characterized. Composite membranes exhibits excellent thermal stability, the swelling degree of the composite membranes are lower than that of the pure SPFPP membrane. UiO-66-NH₂ could improve the water retention capacity of composite membranes, resulting in higher water uptakes of composite membranes than pure SPFPP membranes. This higher water retention capacity could improve the proton conductivity of the membrane under high humidity conditions. The proton conductivity of composite membranes SP/UiO-66-NH₂-0.6 reaches up to 0.179 S/cm under 80 ℃, 100%RH, while the proton conductivity of pure SPFPP membranes is 0.120 S/cm under the same conditions.

CsPbBr₃@TiO₂ Heterojunction Microcrystals Gas Sensor for Low-Concentration H₂S Stability Monitoring at Room Temperature

LU Jianghao, HUANG Sheng, CHEN Lu, CHENG Yongchao, GAO Shasha, TAO Xueyu, GU Xiuquan

2024, 53(10):  1815-1826. 

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Through a simple solution method, TiO(Acac)₂ was used to in-situ coat the all-inorganic perovskite material CsPbBr₃. After heating at 400 ℃, CsPbBr₃@TiO₂ core-shell structure microcrystals were directly prepared. The crystal structure, microscopic morphology, and chemical composition of CsPbBr₃@TiO₂ microcrystals were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). It was confirmed that the in-situ metal oxide coating on the perovskite formed well-dispersed spherical shell structures with sizes of 4~8 μm. A CsPbBr₃@TiO₂ thin film gas sensor was constructed on a fluorine-doped tin oxide (FTO) electrode using spin-coating method. The sensitivity of the sensor to H₂S gas was tested at room temperature. The results show that the sensor has a detection limit of 25 ppb (1 ppb=10^-9) for H₂S gas, with a response and recovery time of 24/21 s to 100 ppb H₂S, and a sensitivity of 0.59. The response curve exhibits good cyclic stability. Moreover, the sensor maintains over 90% stability within 30 d of exposure in air and possesses excellent gas selectivity and humidity resistance. Photoluminescence (PL) spectroscopy, time-resolved photoluminescence (TRPL) spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis), and ultraviolet photoelectron spectroscopy (UPS) were employed to analyze the band positions, charge dynamics, and coordination mechanisms. The sensing mechanism was elucidated using the oxygen adsorption principle. This work provides a new approach for the stable monitoring of low concentrations of H₂S gas at room temperature.